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If you're going the stepped bit route, go with a good product and avoid cheap. I bought a set of stepped bits. Yeah, I can cut a hole up to 1&1/3 inches, but I went with a "discount" set and these things leave major league metal burs. That's not to say I didn't end up with a nice hole, I did. It just took a little more work than I had anticipated. I think next time I'm ready to buy, I'll go with a punch set.

_________________The key to a successful build is to keep the smoke IN the circuit. -Les

I favor bimetal hole saws since they're not too expensive and easy to obtain from a hardware store or a big box store.

A couple of tips, though: 1) Use a drill press if you have one. Not critical, but a bit easier. 2) I tape off the entire surface of the chassis with heavy masking tape, on which I mark all my holes. To keep things symmetrical, I usually draw a grid on the chassis using a tri-square and then mark intersections of lines where holes are to be drilled. Since I have been known to get excited when drilling at first, I now circle all intended drill marks with a red sharpie. 3) Always drill a pilot hole to guide the hole saw's center bit. You can use a center punch to guide the bit, which will (should) keep it from "wandering." The pilot hole needn't be big, just enough to guide the hole saw bit. Most hole saws use a 1/4 inch guide bit, so I drill pilot holes which are 1/8 inch or smaller. 4) ALWAYS use a wood backing block when drilling holes in the chassis. This prevents the chassis from being deformed. Do the same when using the hole saw. 5) I go slow (slow drill speed and light pressure) when drilling into metal. Many guys I know seem to think their drills are hammers or chisels and they'll win a prize for drilling the fastest hole. If you like massive burrs then there's your prize! 6) I clean up the finished hole with a fine-tooth concave file. Burrs are removed by angling the file relative to the surface of the chassis, working from both sides. I sometimes use a Dremel with a small grinder to dress the inside surfaces, especially when the chassis is painted and a good electrical contact is needed.

I go slow (slow drill speed and light pressure) when drilling into metal. Many guys I know seem to think their drills are hammers or chisels and they'll win a prize for drilling the fastest hole. If you like massive burrs then there's your prize!

I think a just got a poor set of stepped bits. I don't use force on the drill and let the bit do its job. I don't have a drill press, to speak of. What I've got is one of those bench top "mount your drill in to it" presses. It's ok for small projects and cases, but not so much for larger cases, more than 3" from edge to center. That's what I get for being cheap! Bargain basement price begets bargain basement quality.

You make all good points, however!

_________________The key to a successful build is to keep the smoke IN the circuit. -Les

I don't mean to throw a wrench into the machinery here but there is one other important factor to consider; alloy content.

When drilling or working aluminum, the alloy is almost as important as the tooling method. For example, I always use 6061-T6 aluminum sheeting for my chassis work. This is because whereas 6061 is not the strongest of the aluminum alloys, it definitely has the best machining characteristics. I have tried to use both 5052 and 5056 but neither one worked very well. Both resulted in burrs, gouges, and difficult filing and me having to clean my mill files about every 5 strokes.

If you're not buying raw sheet but rather formed chassises, give the manufacturer a call. In most instances they will tell you what is the alloy content of their boxes and some will even offer machining tips for working with their products. Never underestimate the power of a simple phone call. You can also do an internet search on the alloy in question and usually find material characteristics and machining information.

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